1. Technical Field
The present invention relates in general to improved disk certification calibration, and in particular to an improved disk drive laser melt bump disk for accurate glide calibration.
2. Description of the Related Art
Generally, a data access and storage system consists of one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, two or three disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
The only other moving part within a typical HDD is the actuator assembly. The actuator moves magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
Typically, a slider is formed with an aerodynamic pattern of protrusions (air bearing design) on its air bearing surface (ABS) that enables the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each platter and flies just over the platter""s surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop directly over the desired track.
The presence of asperities on the surfaces of the disks can have a deleterious effect on the performance of disk drives. For this reason, a glide test is performed on finished disks to detect asperities that might contact the magnetic head flying at its normal height in a disk drive. In the test, a special glide head containing a piezoelectric transducer (PZT) is flown over a disk at an altitude or height that is below the normal drive fly height. Glide head contact with an asperity creates a PZT voltage response that generally scales with increasing size of the asperity. If the voltage response exceeds a predetermined level, the disk is rejected. As such, quantitative glide testing requires calibration of the voltage response with respect to asperity height.
One method of calibrating glide heads uses laser-generated, nano-sized protrusions or laser melt bumps (LMB) on the surface of a disk that can serve as calibration asperities. Laser nano-bump generation is a technique that is used throughout the data storage industry. Flying a guide head over a laser nano-bump whose height is known (e.g., by interference or atomic force microscopy) will thus generate a calibrated PZT response. However, the certainty of the response is much improved by use of statistical averaging methods.
Since the glide certification process is one of the most important steps in fabricating the hard disks of the disk drives, the accuracy of glide certification is the single most important factor that directly affects the yield and, thus, the production is cost of the disks. Prior to the glide certification process on production disks, glide heads are calibrated by flying over the LMB with certain interference heights. Currently, the LMB are made on aluminum-magnesium (AlMg) substrates.
An enlarged isometric view of a single prior art AlMg bump 11 is depicted in FIG. 1. As is typical of AlMg bumps, the perimeter 13 of bump 11 rises slightly above the planar surface of the AlMg disk 15, while the center of bump 11 is a relatively deep parabolic recess 17. Unfortunately, there is a material incompatibility for calibration on AlMg substrates and tests performed on other materials. Moreover, the supply of AlMg substrates used for calibration bump disks in disk manufacturing engineering is limited, such that there is an urgent need to switch all calibration devices from AlMg to another material. Thus, an improved bump disk for accurate glide calibration is needed.
One embodiment of an improved bump disk for accurate glide calibration has a new type of glass laser melt bumps that give the same signal amplitudes as conventional AlMg laser melt bumps for the same bump height. The present invention provides a solution to switch the calibration bumps from AlMg to glass, and can be used in disk manufacturing lines to save 30% on the cost of hard disks from inaccurate glide certification processes. The solution is to trim or burnish away the very top portion (i.e., the low response portion) of the glass bumps. This additional processing step causes the responses from the glass bumps to become very similar to those of the AlMg bumps, thereby enabling glass and AlMg disks to become materially compatible.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the preferred embodiment of the present invention, taken in conjunction with the appended claims and the accompanying drawings.